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ECE 202 - Experiment 3 - PreLab Homework
THE BREADBOARD; DC POWER SUPPLY; RESISTANCE OF METERS;
NODE VOLTAGES AND EQUIVALENT RESISTANCE;
THÉVENIN EQUIVALENT CIRCUIT
YOUR NAME______________________
LAB MEETING TIME______________
Reference: C.W. Alexander and M.N.O Sadiku, Fundamentals of Electric Circuits
Chapters 2, 3 and 4
THE BREADBOARD
1. a) Sketch on the left breadboard lines that illustrate pattern of short connections on the breadboard.
It is enough to draw several examples for each type of connections.
b) Sketch the circuit below on the right breadboard in the manner you would do it with actual
components. Use lines to represent wires, familiar symbols for resistors. Mark the A, B, C, D
and E points of the circuit.
a) Pattern of short connections
b) Connecting the circuit
ECE 202 - Experiment 3 - PreLab Homework
RESISTANCE OF METERS
2. a) A voltmeter is an instrument for measuring the difference in potential energy (voltage) between
two points. Voltage is measured in units of volts (V).
What should be the value of internal resistance of an “ideal” voltmeter (low / medium / high)?
RV = __________________
Why is such voltmeter called ideal? Sketch and explain.
c) An ammeter is an instrument for measuring the current, or rate of flow of charge, through a
circuit. Current is measured in units of amperes (A).
What should be the value of internal resistance of an “ideal” ammeter (low / medium / high)?
RA = __________________
Why is such ammeter called ideal? Sketch and explain.
d) By Ohm’s Law, I1 = V/R.
If we insert a real (not ideal) ammeter, as shown, with internal resistance RA, the current in the
circuit will change to I2. Assume that real ammeter may be substituted with RA in series with
the ideal ammeter.
e) Derive an expression for I2 in terms of the previous I1, R and RA.
I2 (expression) = _____________
f) Determine the value of RA for which I2 = 0.5 I1.
RA (for 0.5 I1) = _____________
ECE 202 - Experiment 3 - PreLab Homework
g) By Ohm’s Law V1 = IR.
If we insert a real voltmeter into the circuit, as shown below, with internal resistance RV, the
voltage will change to V2. Assume that real voltmeter may be substituted with RV in parallel
with the ideal voltmeter.
h) Derive an expression for V2 in terms of V1, RV and R.
V2 (expression) = _____________
i) Determine the value of RV for which V2 = 0.5 V1.
RV (for 0.5 V1) = _____________
ECE 202 - Experiment 3 - PreLab Homework
NODE VOLTAGES
3. You will build the following circuit in the lab. Calculate all node voltages using method of your
choice. You will later compare your calculations to measured values.
Show your work here:
Calculated circuit variables using nominal resistor values: (include units)
VA = ____________
VB = ____________
VD = ____________
VE = ___________
VC = ____________
ECE 202 - Experiment 3 - PreLab Homework
EQUIVALENT RESISTANCE
4. The idea of equivalent resistance is that, as viewed from the external terminals, a circuit consisting
of a number of interconnected resistors can be replaced by one equivalent resistor having a value
equal to the combined effect of all the original resistors. At the external terminals, this equivalent
resistor will be indistinguishable from the original circuit.
Consider the resistor combination within the box in the circuit from part 3. It can be replaced with
a single equivalent resistor Re. In the lab you will do this and observe any change in the remaining
node voltages of the circuit. Calculate the equivalent resistance of the resistor combination inside
the dotted box using their nominal values. Show your work here:
Re = ____________ (kΩ)
THÉVENIN EQUIVALENT CIRCUIT
5. The resistors in the dashed box have been replaced by their equivalent Re and we will now focus
on the elements that were formerly outside the box.
Calculate the Thévenin equivalent circuit of everything to the left of Re. Show your calculations here:
VTh = ____________ (Volt)
RTh = __________ (Ohms)
ECE 202 - Experiment 3 - PreLab Homework
RESISTOR COLOR CODES
Although every effort is made that resistors are placed in the correct bins in the lab, you should
always check their nominal values before using them. Write 5-band colors for the resistors you will
be using in the first lab.
Note #1: In a 5-band resistor notation, band allocation is:
bands 1-3:
significant digits (value)
band 4:
order of magnitude
band 5:
tolerance (in percents)
Note #2: Assume 5% tolerance (although resistors in the lab may have different tolerances).
4.7kΩ _________________________________________________________________
10kΩ _________________________________________________________________
2.6kΩ _________________________________________________________________
1kΩ
_________________________________________________________________
800kΩ _________________________________________________________________
400kΩ _________________________________________________________________
*Tech Notes: Resistors have nominal resistance values which are
written on them or indicated by the color code. The actual
resistor value, however, can be determined only by measurement.
In this homework, use nominal values; in the experimental part,
you will use measured values.
http://en.wikipedia.org/wiki/Electronic_color_code